Which scenario designates an illegal play under the rules?

The scenario that designates an illegal play under the rules is when a served ball is contacted multiple times, which is typically regarded as a fault. In volleyball, the served ball must be hit cleanly and cannot touch any part of the player more than once. If multiple contacts occur, it is ruled as an illegal serve.

The other scenarios described do not constitute illegal plays. A ball that hits the net during a serve is still considered in play, provided it goes over to the opponent's side. Successful spikes are a legitimate offensive action in volleyball. A player intentionally avoiding contact with the net during play is actually following proper rules in terms of court conduct and net play. Thus, the clear violation occurs with the multiple contacts during a serve.